Astronomers report that the Milky Way swallowed a dwarf galaxy about 11.8 billion years ago, an event the team names Low-energy-Kraken-Heracles or LKH. The researchers estimate LKH contained about 500 million solar masses in stars, roughly one quarter of the Milky Way's mass at the time. Using Hubble and Gaia to measure ages, chemical composition and trajectories of stellar clusters in the innermost 20,000 light-years, the team identifies this as the galaxy's earliest-known merger, occurring roughly 2 billion years after the Big Bang. Lead author Davide Massari of INAF said the merger deposited a large volume of stars, interstellar gas and dark matter into the Milky Way; gas collisions likely triggered a burst of star formation while stars passed without direct collisions. The study notes the Milky Way later absorbed Gaia-Sausage-Enceladus about 1.8 billion years after LKH and has been merging with the Sagittarius dwarf over the past roughly 6 billion years. Many stars originating in LKH likely remain buried in the Milky Way's inner regions, but interstellar dust there makes identifying them individually difficult.
![Fig 2 (left) and 5 (right) : Fig. 2 : Toomre diagram for the MSTO sample colour-coded by metallicity. The candidate star is highlighted with a star symbol. The dashed curves indicate the kinematic loci commonly used to distinguish thin-disc, thick-disc, and halo populations based on total velocity with respect to the LSR. Fig. 5: Distribution of the MSTO sample in the [Al/Fe]-[Mg/Mn] plane, colour-coded by metallicity. The black solid lines indicate the empirical separation between Galactic components proposed by Alinder et al. (2026). The candidate is marked with a star symbol.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:cugc4wn2mruqtvx7lm2kztiy/bafkreih7rxafw72ko5t7tjfvzslwc4radgnzxpp5hcnaszjttv3the2yoq)
